1. Field of the Invention
The present invention relates to the field of neuroscience and, more particularly without limitation, to a subfield of neuroprostheses for housing devices in close proximity to the brain.
2. Glossary of Terms and Useful Definitions
The term “electroencephalogram” (“EEG”) refers to voltage potentials recorded from the scalp and encompasses any recordings obtained from a source outside the dura mater. The term “electrocorticogram” (“ECoG”) refers to voltage potentials recorded intracranially, e.g., directly from the cortex. “EKG” is an abbreviation for the term “electrocardiogram,” “EMG” for the term “electromyogram” which records electrical muscle activity, and “EOG” for the term “electrooculogram” which records eye movements.
The term “real-time” as used herein describes a system with negligible latency between input and output.
As used herein, the term “outer table” refers to the outer bony sheet of the skull in contact with the scalp; the term “inner table” refers to the inner bony sheet of the skull in contact with the outermost brain membrane or “dura”; and the term “diploe” refers to the part of the skull between the outer table and inner table that provides nutrients and minerals necessary for developing and maintaining the skull.
3. Description of the Related Art
Humans and animals have several normal states of behavior, such as wakefulness and sleep, as well as multiple sub-states, such as attentive wakefulness and REM sleep. Abnormal states of behavior in humans and animals include reversible states, such as seizures, and progressive irreversible states, such as dementia.
Recent advances in the field of clinical neurosciences have opened a new era for the use of and need for implantable therapeutic devices. For example, the use of prostheses, for the diagnosis or treatment of neurologic illnesses, is rapidly growing and will continue to expand as new applications are found. As new technological developments take place, so does the opportunity to improve current designs or performance, decrease power requirements or cost, or minimize complications associated with chronic implantation. For instance, a device to electrically stimulate brain regions, via chronically implanted electrodes for Parkinson's disease, has been recently approved for commercial use by the Food and Drug Administration. Implantable devices to detect and control abnormal brain states, such as epileptic seizures, are currently under development (see Osorio et al., Epilepsia 39(6):615-627, 1998).
Currently, brain devices, such as the one used for Parkinson's disease, are implanted under the collarbones at a substantial distance from the brain. For example, the use of wires or conductors to carry a signal into or out of the brain, requires a special, time consuming procedure and careful placement of wires and connectors to avoid scalp/skin erosion, a common and serious complication which often requires removal of the device with loss of benefit to the subject. More specifically, such an approach has several significant disadvantages: (i) the long conductors for connecting the device to electrodes implanted in the brain require tunneling under the scalp and skin, thereby requiring prolonged surgical and anesthesia for installation; (ii) the tract along the conductors often becomes infected requiring, in many cases, that the conductors be explanted with consequent cessation of treatment to the subject; (iii) the conductors often erode the overlying scalp, forcing removal of the cables so that healing can take place but, at the same time, removing the means for warning of or treating impending abnormal activities; (iv) the conductors often fracture since they are subjected to torsional and other forces generated by normal head/neck movements with consequent corrective surgery to replace the faulty conductors; and (v) in the case of telemetered signals, closer proximity of the emitter to the receiver would increase fidelity of the transmitted signals and decrease power requirements, hence prolonging battery life and decreasing frequency of surgical replacement procedures.
The placement of prior art brain devices outside the skull, such as in the infra-clavicular regions, is due to lack of space between the brain and the skull to position such devices and also to the inability to convert virtual into real spaces without affecting the integrity of the skull. Indeed, while the brain is closely apposed to the inner table of the skull, leaving no usable space to safely house any device, the skull has several properties that enable conversion of virtual into real space for use of the integrated ergonomic placement of devices. These properties, which have not been heretofore exploited, include:                a) sufficient wall thickness to allow housing of access systems/electronic components partially or completely within the confines of the two tables of the skull;        b) high tensile strength; and        c) semi-circular configuration allowing equal distribution of forces over its surface.In addition, scalp tissue has the elasticity or deformability necessary for accommodation of housing devices.        
Accurate and reproducible prediction of behavioral or biologic signal changes associated with abnormal brain activities has not been generally possible as such events typically occur unpredictably. This limitation has been recently overcome, making it possible to accurately predict various types of brain states, such as epileptic seizures, etc., as taught in U.S. patent application Ser. No. 08/778,771.
Thus, what is needed is a cerebral interface system that permits spacing essential mechanisms, which perform these or other tasks in close proximity to a subject's brain.